The present invention relates to a shaft for golf clubs (hereinafter referred to simply as shaft). More specifically, the present invention relates to a shaft that is 35-50 percent lighter than conventional shafts while providing the same outer diameter and the same characteristics as conventional shafts such as flexural rigidity, flexural strength, torsional rigidity, torsional strength, and crushing strength.
In one type of golf club, a fiber-reinforced composite material (hereinafter referred to as FRP) is used in forming the shaft. In this type of shaft, a fiber-reinforced fiber material is formed by lining up reinforcing fibers in a xe2x80x9cone-directionalxe2x80x9d pre-impregnation (hereinafter referred to as prepregs) and then immersing the aligned fiber material in a resin. The shaft is then formed by wrapping the fiber-reinforced material around a tapered metal mandrel and hardening the composite in a laminated state. This type of golf club shaft is widely used due to its high specific rigidity, specific strength, and the degree of freedom allowed in its design.
FRP shafts often use a two-layer structure to form the reinforced composite. An inner layer is formed of angled fibers (angled layer) and an outer layer is formed from straight fibers (straight layer). In the angled layer, prepregs are glued together so that the reinforcing fibers form angles of +theta; xe2x88x92theta relative to the longitudinal axis of the shaft. In the straight layer, the prepregs are stacked so that the reinforcing fibers are within a +/xe2x88x9220 degree range relative to the longitudinal axis of the shaft.
In recent years, there has been a trend toward creating lighter golf club shafts. By lightening the shaft it is possible to produce a larger xe2x80x9csweet spotxe2x80x9d in the golf club head. With a larger xe2x80x9csweet spotxe2x80x9d in the golf club head, golf clubs can be designed to accompany higher head speeds, longer shafts, and larger heads.
Conventionally, lighter golf club shafts are designed and manufactured by simply reducing the number of straight layers and angled layers that make up the shaft. As a consequence of reducing the number of layers there is a reduction in flexural rigidity, flexural strength, torsional rigidity, torsional strength, and crushing strength. These reductions in strength and rigidity are undesirable.
Alternative methods have been attempted to create lighter shafts which minimize the adverse effects on strength and rigidity. Two methods which provide for a lighter shaft while maintaining flexural rigidity and torsional rigidity are as follows:
(1) reduce the number of straight layers and/or angled layers while also using a reinforcing fiber that has a high elasticity in these layers; and
(2) reduce the thickness of the layers by changing the shape of the shaft itself, primarily by increasing the outer diameter.
In method (1), the flexural rigidity and torsional rigidity are comparable with conventional shafts. However, reinforcing fibers with high elasticity generally have low strength. Golf club shafts designed according to method (1) result in flexural and torsional strengths which are the same as, or even lower than, golf clubs shafts which simply have the number of layers reduced.
In method (2), increasing the outer diameter near the grip is effective in maintaining flexural rigidity. However, the increased grip diameter results in a golf club shaft that is difficult to handle, making the arrangement impractical.
Japanese laid-open utility model publication number 62-33872 discloses a method for improving the torsional rigidity and torsional strength in FRP shafts. According to this method, an FRP shaft includes angled layers and straight layers which are formed with the angled layer as the outermost layer. However, the finishing process of the FRP shaft, i.e., polishing and the like, can result in a loss in the angled layer. The thickness of the angled layer is needed to maintain torsional rigidity and torsional strength. Thus, FRP shafts made according to this method do not have consistent quality. In addition, this method does not provide for a lighter FRP shaft.
Japanese laid-open patent publication number 8-131588 provides for another method of improving an FRP shaft. According to this method, an FRP shaft includes (starting from the inner most layer): a thin hoop layer, a straight layer, and an angled layer. As in the method previously described above, the finishing process of the FRP shaft, i.e., polishing and the like, can result in the loss of the angled layer needed to maintain torsional rigidity and torsional strength. Thus, FRP shafts made according to this method do not have consistent quality and do not result in a lighter FRP shaft.
It is an object of the present invention to provide a golf club shaft which overcomes the drawbacks in the prior art.
It is another object of the present invention to provide a lighter golf club shaft that overcomes the drawbacks of the prior art.
It is yet another object of the present invention to overcome the problems of the prior art and to provide a shaft that is 35-50% lighter than a conventional shaft.
It is a further object of the present invention to overcome the problems of the prior art and to provide a shaft that is 35-50% lighter than a conventional shaft while maintaining the same outer diameter as a conventional shaft.
It is another object of the present invention to overcome the problems of the prior art and to provide a shaft that is 35-50% lighter than a conventional shaft while maintaining the flexural rigidity, flexural strength, torsional rigidity, and torsional strength of a conventional shaft.
It is yet another object of the present invention to overcome the problems of the prior art and to provide a shaft that is 35-50% lighter than a conventional shaft while maintaining the outer diameter, flexural rigidity, flexural strength, torsional rigidity, and torsional strength of a conventional shaft.
It is another object of the present invention to provide a light-weight golf club shaft that is formed by laminating a plurality of fiber-reinforced composite materials. The laminate is made by forming the following layers in sequence starting with the inner most layer: a first angled layer; a first straight layer; a second angled layer; and a second straight layer. Each layer is a fiber-reinforced composite material. The laminated layers extend over the entire length of the shaft.
It is another object of the present invention to provide a light-weight golf club shaft formed by laminating a plurality of fiber-reinforced composite materials, the laminate being made by forming a first angled layer, a first straight layer formed on the first angled layer; a second angled layer formed on the first straight layer, and a second straight layer formed on the second angled layer. Each layer is a fiber-reinforced composite material. The laminated layers extend over the entire length of the shaft. The second angled layer has a thickness of 0.04-0.10 mm, and reinforcing fibers contained therein have an orientation of 35-75 degrees relative to the longitudinal direction of the shaft. The shaft has a torsional strength of at least 120 kgfxc3x97mxc3x97degrees (1200 Nxc3x97mxc3x97degrees) and a weight of 30-40 g.
Briefly stated, the present invention provides a golf club shaft that is 35-50 percent lighter than a conventional shaft while maintaining the outer diameter and structural characteristics of conventional shafts. The shaft has at least four layers of fiber reinforced material. The fiber reinforced layers are from innermost to outermost: a first angled layer; a first straight layer; a second angled layer, and a second straight layer. The angled layers are formed by bonding together two materials, each with fibers aligned in different directions. The second angled layer maintains the proper strength and rigidity of the shaft while keeping the shaft as light weight as possible. Aligning the second layer""s fibers at an angle of 35-75 degrees with respect to the longitudinal direction of the shaft ensures proper weight and strength characteristics of the shaft. The resulting shaft is light-weight and exhibits the flexural rigidity, flexural strength, torsional rigidity, torsional strength, and crushing strength of conventional shafts.
According to an embodiment of the present invention, there is provided a light-weight golf club shaft comprising: a first angled layer, a first straight layer formed on said first angled layer, a second angled layer formed on said first straight layer, a second straight layer formed on said second angled layer, said shaft having a length along a longitudinal direction, each of said layers extend over said length of said shaft and includes fiber-reinforced composite material, said fiber-reinforced composite material containing reinforcing fibers, said reinforcing fibers of said second angled layer being oriented at an angle relative to said longitudinal direction of said shaft, and said second angled layer being selected to provide said shaft with a torsional strength of at least 120 kgfxc3x97mxc3x97degrees and a weight of from 30 to 40 g.
According to another embodiment of the present invention, there is provided a light-weight golf club shaft, said shaft having a length along a longitudinal direction, comprising: a first angled layer, a first straight layer formed on said first angled layer, a second angled layer formed on said first straight layer, a second straight layer formed on said second angled layer, each of said layers extend over said length of said shaft and include fiber-reinforced composite material, said fiber-reinforced composite material containing reinforcing fibers, said reinforcing fibers of said second angled layer oriented at an angle in a range of from 35 to 75 degrees relative to said longitudinal direction of said shaft, said second angled layer has a thickness in a range of from 0.04 to 0.1 mm, said shaft has a small-diameter end and a large-diameter end, said first angled layer has a first thickness near said small-diameter end of said shaft, said first angled layer has a second thickness near said large-diameter end of said shaft, said first thickness is substantially twice said second thickness, and said layers are effective to provide said shaft with a torsional strength of at least 120 kgfxc3x97mxc3x97degrees and a weight of from 30-40 g.
According to a method of the present invention, there is provided a method forming a golf club shaft around a mandrel having a length along a longitudinal axis, the steps comprising: forming a first reinforcement layer from a first fiber material, said first fiber material having fibers aligned along a single direction, forming a first angled layer from second and third fiber material, said second and third materials having fibers aligned along a single direction, bonding said second and third materials together to form said first angled layer, such that said fibers of said second material form a first angle with said fibers of said third material, forming a first straight layer from a fourth fiber material, said fourth fiber material having fibers aligned along a single direction, forming a second angled layer from fifth and sixth fiber material, said fifth and sixth materials having fibers aligned along a single direction, bonding said fifth and sixth fiber materials together to form said second angled layer, such that said fibers of said fifth and sixth material form a second angle in the range of from 70-150 degrees and said second angled layer has a thickness in the range of from 0.04 to 0.1 mm, forming a second straight layer from a seventh fiber material, said seventh fiber material having fibers aligned along a single direction, forming a second reinforcement layer from an eighth fiber material, said fiber material having fibers aligned along a single direction, wrapping said first reinforcement layer around said mandrel such that said fibers of said first reinforcement layer are aligned 90 degrees with respect to said longitudinal axis, wrapping said first angled layer around said first reinforcement layer such that said first angle of said fiber material of said first angled layer is bisected by said longitudinal axis, wrapping said first straight layer around said first angled layer such that said fibers of said first straight layer are aligned with said longitudinal axis, wrapping said second angled layer around said first straight layer such that said second angle of said fiber material of said second angled layer is bisected by said longitudinal axis, wrapping said second straight layer around said second angled layer such that said fibers of said second straight layer are aligned with said longitudinal axis, wrapping second reinforcement layer around said second straight layer to form a layered wrap, such that said fibers of said second reinforcement layer are aligned with said longitudinal axis, curing said layered wrap in an oven to form a cured shaft, removing said mandrel from said cured shaft, and trimming ends said cured shaft to produce said golf club shaft.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.